Thermodynamics - Weighing an aquarium

During an ecology experiment, an aquarium half filled with water is placed on a scale. The scale reads 195N.

a) a rock weighing 8N is added to the aquarium. If the rock sinks to the bottom of the aquarium, what will the scale read?

b) The rock is removed from the aquarium and the amount of water is adjusted until the scale again reads 195N. a fish weighing 2N is added to the aquarium. What is the scale reading with the fish in the aquarium?

would i use the equation for finding the buoyant force which = pVg coz i think its asking for the pressure the rock experiences in water which imo is buoyant force..